1. Field of the Invention
The present invention relates to a method for generating a feedback message and reducing overheads in a wireless portable communication system, and more particularly, it relates to a repeat request algorithm for reducing overhead by using an Automatic Repeat reQuest (ARQ) feedback message in a newly defined ACKnowledgment (ACK) MAP.
2. Description of the Related Art
In a wireless portable Internet system, an ARQ algorithm has been developed to minimize an error rate and enhance error correction in data transmission.
The ARQ algorithm is used as a method for retransmitting a damaged data packet with reference to a feedback message (ACK and Negative ACK (NACK)) of each transmitted data packet or in consideration of timeout when the corresponding feedback message is not received.
FIG. 1 shows a block diagram illustrating an ARQ transmitter and an ARQ receiver.
A transmitter 10 transmits a Protocol Data Unit (PDU) to a receiver according to an ARQ mechanism. The PDU is generated from a Service Data Unit (SDU) that is generated from an upper layer 11 and stored in a buffer 12.
An ARQ receiver 23 transmits a feedback message for ARQ to the transmitter 10. The feedback message for ARQ includes an ACK message or a NACK message according to success or failure of the PDU transmission and is used for error correction in the mobile Internet system.
An ARQ transmitter 13 retransmits the corresponding PDU or transmits a discard message to the ARQ receiver 23 in response to the ACK message or the NACK message.
Hence, the result of ARQ that indicates success or failure of transmission is available for transmitter 10 to analyze data transmission efficiency according to the receiver or a channel quality. Quality of Service (QoS) analysis and scheduling can be achieved by referring to the data transmission efficiency.
FIG. 2 is a diagram illustrating a signal flow according to a conventional ARQ method.
When the transmitter 10 transmits a data packet to the receiver, the receiver sends an ACK message as the feed back message for ARQ to the transmitter after receiving the data packet. The ACK message includes a cumulative ACK message and a selective ACK message, which will be stated later.
The ARQ receiver 23 sends the ACK message to the ARQ transmitter 13 when the ARQ receiver 23 successfully receives the data packet, but the ARQ receiver may fail to receive the data packet when the data packet is lost because of a bad channel quality.
The transmitter may not also receive an ACK message from the ARQ receiver 23 when the ACK message is lost due to the bad channel quality. Once the data packet or the ACK message is lost, it is preferable for the ARQ receiver to discard the corresponding data packet after a predetermined lifetime so that the ARQ transmitter may not infinitely wait for a response or retransmit the data packet.
Conventionally, the ARQ transmitter 13 sends a discard message to the ARQ receiver when the data packet or the ACK message is lost on the channel and therefore the transmitter 10 receives no ACK message for a predetermined lifetime, in step S1.
The ARQ receiver 23 sends a discard response message in response to the discard message, and discards the transmitted data packet in step S2.
FIG. 3 to FIG. 5 respectively show formats of the ARQ feed back message in the wireless portable Internet system.
FIG. 3 shows a selective ACK message.
In FIG. 3, it is assumed that a Medium Access Control (MAC) layer PDU (MAC PDU) containing 12 sequence blocks, is transmitted to the receiver and errors occur in the fourth, seventh, eighth, and twelfth sequence blocks in the wireless portable Internet system. The ARQ receiver sends an ACK MAP as the feed back message for ARQ in response to the transmitted MAC PDU. The ACK MAP maps a receipt success into 1 and a receipt error or failure into 0. The ARQ transmitter receives the ACK MAP and retransmits blocks of sequence numbers which are mapped into 0 to the ARQ receiver.
FIG. 4 shows a cumulative ACK message.
When errors occur in the Block Sequence Numbers (BSNs) 4,7, 8, and 12 of the MAC PDU as shown in FIG. 3, the ARQ receiver generates a corresponding feedback message for ARQ by recording the first sequence of successive blocks (BSNs 1,2, and 3) transmitted without an error in the feedback message for ARQ.
The ARQ receiver then sends an ACK to inform that the ARQ receiver successfully received the BSNs 1,2, and 3, and the ARQ transmitter retransmits the blocks from the BSN 4 to BSN 12 of the MAC PDU as shown in FIG. 4.
FIG. 5 shows a selective and cumulative ACK message.
Although the selective ACK message of FIG. 3 is efficient because it only retransmits the blocks with an error, a data processing time and the size of the ACK MAP are problematically increased. The cumulative ACK message shown in FIG. 4 requires less capacity for the feedback message and provides a very fast data processing time, but increases the size of data to be retransmitted.
In FIG. 5, the ARQ receiver requests retransmission by sending the ARQ transmitter an ACK feedback message containing the successfully received BSNs (BSNs 1,2, and 3) and an ACK MAP remapped from BSN 4 to BSN 12 by taking advantages of the selective ACK message and the cumulative ACK message.
However, the foregoing feedback message for ARQ is not efficient in the wireless portable Internet system since a sequence of successive blocks forms a PDU, and success or failure of data transmission occurs in each PDU.
In other words, the conventional bitmap-type ACK MAP maps success and failure of each BSN, thereby increasing an overhead.
Therefore, an efficient method for transmitting the feedback message for ARQ without increasing the overhead is needed in the wireless portable Internet system.